1. Field of the Invention
The present invention relates generally to a method and apparatus for bonding together elements or parts (members in more general sense) of semiconductor devices or the like by making use of a laser beam. More particularly, the invention is concerned with a bonding method and an apparatus for bonding and evaluating the quality of the bonds formed.
2. Description of the Related Art
For a better understanding of the invention, the technical background will first be described in some detail.
FIG. 4 is a vertical sectional view showing an exemplary structure of a bonding apparatus known heretofore and referred to as a tape automated bonding or TAB apparatus, which is disclosed in Japanese Unexamined Patent Application Publication No. 151464/1983 (JP-A-58-151464). The bonding apparatus includes a base 101 having a top portion formed with a recess in which a follower ball receiving fixture 103 having a substantially hemispherical bearing cavity is fitted. A follower ball 105 having a substantially hemispherical shape complementary to that of the cavity is universally rotatable within the semicircular cavity formed in the ball receiving fixture 103. The hemispherical follower ball 105 has a top surface having a hole in which a supporting stage 107 made of an insulation material is fixedly secured. The supporting stage 107 is adapted for supporting fixedly thereon a semiconductor chip 111 having a plurality of bumps 111A as the parts or members to which lead terminals mentioned below are to be bonded. Disposed above and in opposition to the supporting stage 107 is a bonding tool 113 which can be moved in the vertical direction toward and away from the supporting stage 107. Additionally, there is disposed above the supporting stage 107 in the vicinity of the semiconductor chip 111 a lead frame 115 having a plurality of lead terminals 115A which are to be bonded to the bumps of the semiconductor chip 111 mentioned above.
In operation of the bonding apparatus of the structure described above, the semiconductor chip 111 is fixedly secured onto the supporting stage 107 in such a disposition that a surface of the chip 111 having the bumps 111A is exposed upwardly. Subsequently, the lead frame 115 having a lead terminals 115a is disposed on the semiconductor chip 111 so that terminal edge portions of the lead terminals 115A exposed by partially delaminating a protection tape 117 covering the corresponding surface of the lead frame are brought into contact with the bumps 111A, respectively, of the semiconductor chip 111. Thereafter, the bonding tool 113 is lowered to a position where the terminal edge portions of the lead terminals 115A are pressed against the bumps 111A, whereon a bottom tip portion of the bonding tool 113 is heated to weld the terminal edge portions of the lead terminals 115A to the corresponding bumps 111A simultaneously. In that case, when the lead frame 115 does not extend precisely parallel to the top surface of the semiconductor chip 111 but is slightly inclined relative to the latter, gaps will appear between some of the plural lead terminals 115A and some of the bumps 111A, i.e., an unsatisfactory contact state between the lead terminals 115A and the bumps 111A. In that case, the follower ball 105 of the substantially hemispherical shape is caused to rotate correspondingly within the cavity 103 of the complementary shape, following the pressure exerted by the bonding tool 113, to thereby adjust the disposition of the semiconductor chip 111 such that the top surface thereof extends essentially parallel to the lead frame 115, whereby close or intimate contact is established between the lead terminals 115A and the bumps 111A.
The known bonding apparatus for bonding together simultaneously a plurality of the lead terminals 115A and a plurality of bumps 111A en bloc as described above can certainly operate satisfactorily when the number of the lead terminals and the bumps to be bonded together is relatively small. However, when the number of the lead terminals and the bumps increases, in a semiconductor device of high integration density, it becomes very difficult to realize close contact between all the lead terminals 115A and all the corresponding bumps 111A in a satisfactory manner notwithstanding the adjustment between the lead frame 115 and the semiconductor chip 111 by means of the follower ball adjustment mechanism. In other words, a great difficulty is encountered in realizing bonding of high or satisfactory quality between the lead terminals 115A of the lead frame and the corresponding bumps 111A of the semiconductor chip without reduced yield.
Besides, the known bonding apparatus such as described above is not capable of inspecting the state of the bond as formed. Consequently, after the bonding process, the semiconductor chip 115 having the lead terminals 115A bonded thereto has to be transported to another place where an inspection apparatus or equipment is installed for inspecting the quality of the bond. Thus, a time-consuming procedure is involved for determining the quality of the bond, degrading the efficiency of manufacture of the semiconductor devices as a whole.